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Coil dying?

Hello all,

When a coil fails, does it die immediately? Or does it show 'symptoms' for a while? I am still trying to fine the source of my electrical gremlin (1980 R100 point system; two coil). I have a very sporadic issue where, at highway speed, the GEN light suddenly comes on brightly; the tach goes crazy and the engine begins to run very roughly...Then the light goes off and everything is fine.6

I have cleaned connections, found no damaged wiring, put on a new condenser and voltage regulator. It doesn't seem to be a charging issue...more like I lose energy to the ignition system,..and it is so unpredictable. Sometimes after a few minutes riding..other times after hours...or not at all?

Seems to me that a basic problem would be grounds. You can loose the charging system and end up just running on the battery. If the ground for the battery were to be flaky, your ignition could falter. Be sure all of your grounds are fine. You could have a pinched wire somewhere or something around the coils is touching the tank in certain situations.

Have you cleaned the tower connections where the spark plug wires insert? Have you measured the resistance from one spark plug cap to the other? Should be 20-22K ohms. That will be a static reading, but something to check.

The kill switch is next on my 'contacts needing cleaning' list. At least, when I get this figured out, I'll know that my wiring system is clean and tight.

Last week I thought I had found the issue...I saw that my electric tach would go crazy at the same time the GEN light would flash...Then, the tach stuck at 3000 RPM and wouldn't budge. When I turned the ignition off, it went back to zero...but then the next time I rode it went to 2500 and stuck again...So I unhooked the tach from the coil, and all seemed well...until about an hour of riding, and I had another 'episode'...So strange...

Coil failures can be intermittent, they do not necessarily die a sudden and complete death.

Coils 101:
Internally, the windings can "open" - meaning no current flow through that section.
Or they can "short" - meaning the current is either going somewhere it shouldn't be (like to ground, or flash over to another section of the windings).
The insulation on the wires is a very thin coating of high-temperature semi-flexible enamel; this can degrade over time and cause internal intermittent shorting.
The internal connections to the coil terminals - on both the primary (+12 volts & ground) and secondary (sparkplug tower) sides can crack and break; the secondary (high) voltage can sometimes jump the break and fire the plug, though not as efficiently.
If the tach is receiving a voltage that is not correlated to the engine RPM, then the coil (or coils) become suspect; likewise if the return path (ground) is faulty, then a proper voltage is not routed the way the designers intended and the tach shrugs its shoulders in confusion.
One popular check is to closely view the towers and plug wires at night or in a very dark garage - you may see arcing in the form of tiny bluish-white sparks or corona around the towers or plug wires.
I don't know if a faulty spark plug cap might also cause the tach to behave erratically, but if they're the same age as the other components, don't ignore them: they're continually exposed to heat, vibration, and weather.

You mentioned a new condenser (hopefully a real one, not a knock-off copy); are the points themselves in good condition? Is the little points wire OK too, securely clamped in the terminal, not caught by the points arm (flat spring) where the insulation may be damaged, and is it not squished by the septum (metal wall) of the points cavity? Does the points plate advance easily AND then come back to the idle position? Those two little springs back there also degrade over time, but I don't think this would cause a tach hangup.

'Coils 101' was very informative....These don't show any external cracking or damage, but they Are the original 32 year old units. Might not hurt to refresh...
The point system checks out as suggested.

Thanks for all the excellent advice. Riding weather is (finally) here, and I want the best to get me up to Panguich, Utah and then to Paonia....plus many miles between....

Well, it looks like 'Global Rider hit the nail...My ignition switch seems to be gone. When the engine is idling and I reach behind the switch and even lightly wiggle the wires, the GEN light flashes and the engine begins to sputter and cut out.....

I am thinking about replacing the key switch with a hidden toggle, but need to deduce how to do that....

t seems to be the terminals at the back. Today, on a hunch I wiggled the terminals at the back and got the exact same symptoms I have been experiencing..
The wiring part of the switch is 'dimpled' on...Not surIe how to remove it without destroying it..?

Don't know if this is of any help to you or not but I spent all day yesterday chasing a gremlin that I thought was the ignition switch but turned out to be the starter relay.

The hot red wire that feeds the ignition (terminal 30 on my bike) appeared to have voltage off/on but was acting strange. I finally started using a test light instead of a multimeter and noticed that even thought I had 13+ volts at the switch there wasn't enough juice to light the test light. Working backwards I found that the internal jumper in the starter relay was bad.

I'm not saying this is your problem but the failure mode could potentially cause the problems you describe. (Mine "failed" when inducing a hirer load across the wire by flicking on the high beams.